Waste-Heat Recovery System in Oil-Cooled Gas Compressor

ABSTRACT

The purpose of the present invention is: to enable hot water at a required temperature to be supplied, even in cases when compressor load factor is low; to suppress heat dissipation from a waste-heat recovery device; and to improve waste-heat recovery rate. A waste-heat recovery system in an oil-cooled gas compressor is provided with: a compressor main body (3); an oil separator (6); gas piping (8) which supplies, to a demanded destination compressed gas separated from oil by the oil separator; oil piping (7) which returns, to the compressor main body, the oil separated by the oil separator; and a waste-heat-recovery heat exchanger (10) which recovers heat from the compressed gas and/or the oil. The waste-heat recovery system is also provided with: a hot-water storage tank (19); circulation circuits (17, 18) in which a heat medium is made to circulate between the waste-heat recovery heat exchanger and the hot-water storage tank; a circulation pump (22) provided to these circulation circuits; and a control device (32) which, in cases when the temperature of the oil or the compressed gas subjected to heat exchange in the waste-heat-recovery heat exchanger is equal to or less than the temperature of the hot water in the hot-water storage tank, stops the circulation pump or reduces the rotational frequency of the circulation pump.

TECHNICAL FIELD

The present invention relates to a waste-heat recovery system in anoil-cooled gas compressor, particularly relates to a system ofrecovering waste-heat from an oil-cooled air compressor.

BACKGROUND ART

It is said that combined energy consumed by a gas compressor of an aircompressor or the like corresponds to 20 through 25% of an energyconsumed by a total of a plant and an effect of recovering waste-heatfrom the gas compressor is significant. Particularly, it is anticipatedthat utilization of waste-heat from a gas compressor is going to beregarded to be more and more important in the future also for achievinga target of reducing a CO₂ emission amount originated from the globalwarming problem.

A gas compressor is configured by a compressor main body for compressinggas of air or the like, a cooling system for absorbing heat generated bya compressive operation, a motor which is a driving power source of thecompressor and the like. Further, in a gas compressor, when motor inputpower is regarded as 100%, an amount of heat absorbed in the coolingsystem corresponds to 90% or more of the motor input power, the amountof heat is ordinarily emitted to external air, and a very large amountof energy is emitted to the atmosphere. Although high efficiencyformation of the compressor main body or the motor is promoted forreducing the emitted heat amount, its effect is limited to several %,and it is requested to effectively utilize the waste-heat from the gascompressor.

With regard to effective utilization of the waste-heat from the gascompressor, there are cases of utilization for heating, utilization forhot water, utilization for preheating of water fed to a boiler and thelike.

Incidentally, there are background arts of this kind described inJapanese Patent No. 4329875 (Patent Literature 1) and JapaneseUnexamined Patent Application Publication No. 2012-67743 (PatentLiterature 2).

According to the background art described in Patent Literature 1, acompressor is driven by using steam, and consumption energy of a boileris reduced by utilizing heat generated at the compressor for preheatingwater (feed water) supplied to the boiler.

According to the background art of Patent Literature 2, awaste-heat-recovery heat exchanger is provided to an oil-cooled gascompressor, and waste-heat from oil or the like heated by cooling thecompressor is enabled to recover.

CITATION LIST Patent Literature

Patent Literature 1: Japanese Patent No. 4329875

Patent Literature 2: Japanese Unexamined Patent Application PublicationNo. 2012-67743

SUMMARY OF INVENTION Technical Problem

According to the background art of Patent Literature 1, the heatgenerated at an air compressor is utilized for preheating the feed waterof the boiler, the background art includes a single water cooling systemas a cooling system of the air compressor, the heat generated at the aircompressor is absorbed by water of the water cooling system, and bymixing the water a temperature of which is elevated by the heat with thefeed water to the boiler, a temperature of the feed water to the boileris elevated, and consumption energy of the boiler is reduced.

According to the background art of Patent Literature 1, although thetemperature of water replenished to a feed water tank can be elevated bythe heat generated by the air compressor, the temperature of thereplenished water becomes a temperature lower than a deliverytemperature of the air compressor by several tens degrees even under acondition of reducing the water amount to an extreme. Further, the lowerthe load factor of the compressor, the lower the temperature of thereplenished water.

Therefore, according to the waste-heat recovery system described inPatent Literature 1, although the waste-water recovery system can beutilized for a system in which a temperature of water of the replenishedwater or the like may simply be elevated by utilizing the compressorwaste-heat, in a case where the supplied hot water has a lower limit ina requested hot water temperature, or under a condition in which a lowerlimit of the requested hot water temperature is lower than the deliverytemperature of the compressor only by several degrees, there poses aproblem that the hot water having a requested temperature cannot be fed.Also, there poses a problem that when the water amount is reduced forelevating the temperature of the replenished water, a heat exchange rateis deteriorated as well.

According to the background art of Patent Literature 2, although in thewaste-heat-recovery heat exchanger, the cooling water is heated bysubjecting the oil at a high temperature flowing in an oil piping andcompressed air at a high temperature flowing in a gas piping, and thecooling water from the waste-heat recovery apparatus to heat exchange,no consideration is given to heat emitted from the waste-heat-recoveryheat exchanger in a case where the oil-cooled gas compressor is broughtinto an unload operation (no-load operation) or a stoppage state.Therefore, in a case where the temperature of the cooling water (hotwater) of the waste-heat recovery apparatus is high, there poses aproblem that heat is emitted from a side of the waste-heat recoveryapparatus when the oil-cooled gas compressor is brought into the unloadoperation or the stoppage state, and the waste-heat recovery rate isdeteriorated.

It is an object of the present invention to provide a waste-heatrecovery system in an oil-cooled gas compressor which can supply hotwater at a requested temperature, and which can improve the waste-heatrecovery rate by restraining the heat emitted from the side of thewaste-heat recovery apparatus even in the case where the compressor loadfactor is low.

Solution to Problem

In order to resolve the problem described above, the present inventionis a waste-heat recovery system in an oil-cooled gas compressorincluding a compressor main body, an oil separator for separating oilfrom compressed gas delivered from the compressor main body, a gaspiping for sending the compressed gas separated from the oil by the oilseparator to a demanded destination, an oil piping for returning the oilseparated by the oil separator to the compressor main body, and awaste-heat-recovery heat exchanger for recovering heat from at leasteither of the compressed gas flowing through the gas piping or the oilflowing through the oil piping, further including a stored hot watertank for storing the heat from the waste-heat-recovery heat exchanger ina form of hot water, a circulation circuit for circulating a heat mediumbetween the waste-heat-recovery heat exchanger and the stored hot watertank for moving the heat received from the waste-heat-recovery heatexchanger to the stored hot water tank, a circulation pump provided atthe circulation circuit, and a control device for controlling to stopthe circulation pump or reduce the rotational frequency thereof in acase where a temperature of the oil or the compressed gas subjected toheat exchange by the waste-heat-recovery heat exchanger is equal to orlower than a temperature of the hot water in the stored hot water tank.

Advantageous Effects of Invention

According to the present invention, there can be provided a waste-heatrecovery system in an oil-cooled gas compressor which can supply hotwater at a requested temperature, and a waste-heat recovery rate can beimproved by restraining heat emitted from a side of the waste-heatrecovery apparatus even in a case where a compressor load factor is low.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a system diagram showing a first embodiment of a waste-heatrecovery system in an oil-cooled gas compressor according to the presentinvention.

FIG. 2 is a diagram showing a relationship between a cooling wateramount when a temperature of compressed gas delivered from a compressormain body is regarded as 100 ° C., and cooling water is made to flow toa waste-heat-recovery heat exchanger only once, and a temperature on anoutlet side of the waste-heat-recovery heat exchanger of cooling waterflowed in the system shown in FIG. 1.

FIG. 3 is a diagram showing a relationship between a cooling wateramount when a temperature of compressed gas delivered from a compressormain body is regarded as 100 ° C., and cooling water is made to flow toa waste-heat-recovery heat exchanger only once and a waste-heat recoveryrate by the cooling water flowed in the system shown in FIG. 1.

FIG. 4 is a system diagram showing a second embodiment of a waste-heatrecovery system in an oil-cooled gas compressor according to the presentinvention.

DESCRIPTION OF EMBODIMENTS

An explanation will be given of a specific embodiment of a waste-heatrecovery system in an oil-cooled gas compressor of the present inventionin reference to the drawings as follows. In the respective drawings,portions attached with the same notations designate the same portions orcorresponding portions.

First Embodiment

An explanation will be given of the first embodiment of the waste-heatrecovery system in the oil-cooled gas compressor according to thepresent invention in reference to the system diagram shown in FIG. 1.

In FIG. 1, numeral 3 designates a compressor main body, and according tothe present embodiment, the compressor main body is configured by anoil-cooled screw air compressor. When the compressor main body 3 isdriven by a motor 4, gas (air) sucked into a compressor unit 20 issucked into the compressor main body 3 via a suction filter 1 and asuction throttle valve 2, thereafter, compressed and delivered, andflows into an oil separator (oil tank) 6. Numeral 5 designates adelivery temperature sensor (compressor main body outlet temperaturesensor) (T1) for detecting a temperature of compressed gas (compressedair) delivered from the compressor main body 3. After the temperature isdetected by the delivery temperature sensor 5, the compressed gas flowsinto the oil separator 6.

The compressed gas which flows into the oil separator 6 is mixed withoil (lubricant), in the oil separator 6, the compressed gas and the oilare centrifugally separated, the compressed gas flows out from a gaspiping (air piping) 8 at an upper portion of the oil separator 6 andflows into a waste-heat-recovery heat exchanger 10 configured by awater-cooled heat exchanger. The oil stored to a lower portion of theoil separator 6 flows out from an oil piping 7, flows to a side of thewaste-heat-recovery heat exchanger 10 in a case where the oiltemperature is high, and bypasses to flow to a side of the oil filter 16in a case where the oil temperature is low by a temperature controlvalve 9. The oil passing through the oil filter 16 is configured to flowinto the compressor main body 3 again.

The waste-heat-recovery heat exchanger 10 is connected to a stored hotwater tank unit (waste-heat recovery apparatus) 23. In a case where thestored hot water tank unit 23 is operated, a heat medium (fluid such aswater) is circulated to the waste-heat-recovery heat exchanger 10 viacirculation pipings (heat medium inlet piping 17 and heat outlet piping18) and a heat amount of compression heat generated at the compressormain body 3 is configured to recover by the stored hot water tank unit23 by making the heat medium flow from the heat medium inlet piping 17to the waste-heat-recovery heat exchanger 10 and recovering the heatmedium as the heat medium a temperature of which is elevated from theheat medium outlet piping 18.

That is, according to the waste-heat-recovery heat exchanger 10, theheat medium is configured to be heated and the compressed gas and oilare configured to be cooled by subjecting the oil at the hightemperature flowing through the oil piping 7 and the compressed gas atthe high temperature flowing through the gas piping 8, and the heatmedium from the stored hot water tank unit 23, to heat exchange.

The waste-heat-recovery heat exchanger 10 is arranged in a waste-heatrecovery unit 21. Further, the stored hot water tank unit 23 is providedwith a hot-water storage tank 19 for storing water (as water, a case ofhot water is included), and the hot-water storage tank 19 is connectedwith a water inlet piping 27 for supplying water, and a hot water outletpiping 28 for sending water the temperature of which is elevated (hotwater) by the hot-water storage tank 19 to a hot water supplydestination. Further, a water-to-water heat exchanger 24 is installed inthe hot-water storage tank 19, and a temperature of water in thehot-water storage tank 19 is configured to be elevated by subjecting theheat medium flowing in the circulation pipe and water (hot water) in thehot-water storage tank 19 to heat exchange.

Further, a circulation pump 22 for circulating the heat medium isprovided at the circulation pipings. According to the presentembodiment, the circulation pump 22 is installed at the heat mediuminlet piping 17 in the stored hot water tank unit 23, but thecirculation pump 22 may be installed at the heat medium outlet piping18. The heat medium can be circulated to the waste-heat-recovery heatexchanger 10 and the hot-water storage tank 19 by a number of times bythe circulation pump 22 via the circulation pipings 17 and 18. Thereby,a temperature of water in the hot-water storage tank 19 can be elevatedto a predetermined temperature which is previously determined. Also,even in a case where the load factor of the air compressor is small, thedelivery temperature of the air compressor can be maintained basicallyregardless of the load factor, and therefore, hot water at a requestedtemperature can be supplied regardless of the load factor of the aircompressor. Therefore, even in a case where there is the requested hotwater temperature lower limit and in a case where the requested hotwater temperature lower limit is lower than the compressor deliverytemperature only by several degrees, the hot water at the requestedtemperature can be supplied regardless of the load factor of thecompressor.

An air cooling heat exchanger 13 is provided on a downstream side of thewaste-heat-recovery heat exchanger 10, and the compressed gas and theoil passing through the waste-heat-recovery heat exchanger 10 areconfigured to also pass through the air cooling heat exchanger 13. Thatis, the compressed gas and the oil flow into the air cooling heatexchanger 13 after being cooled by the circulating heat medium at thewaste-heat-recovery heat exchanger 10, or in a state of not beingsubjected to heat exchange with the heat medium in a case where thecirculating pump 22 is stopped. In the air cooling heat exchanger 13,the compressed gas and the oil are configured to be able to be cooled bycooling wind blown by a cooling fan 14.

Numeral 15 designates a fan motor for driving the cooling fan 14, and isconfigured to be able to control the rotational frequency by an inverter29. Therefore, in a case where temperatures of the compressed gas andthe oil coming out from the waste-heat-recovery heat exchanger 10 arehigher than a predetermined temperature, the compressed gas or the oilare configured to be able to be supplied by bringing the temperaturesinto a predetermined range by controlling the rotational frequency ofthe cooling fan 14 in accordance with the temperatures.

The compressed gas coming out from the air cooling heat exchanger 13 issupplied to a demanded destination at outside of the compressor unit 20,and the oil is injected into the compressor main body 3 via the oilfilter 16 after being confluent with other oil in a case where there isother oil bypassed by the temperature control valve 9.

Next, a detailed explanation will be given of a control of supplying thecompressed gas or the oil after bringing the temperatures to a desiredtemperature by controlling the rotational frequency of the cooling fan14.

Numeral 30 designates a control device for controlling the rotationalfrequency of the fan motor 15, and to the control device 30, deliverytemperature information from the delivery temperature sensor 5,temperature information of compressed air (compressed, gas) from atemperature sensor (gas temperature sensor) (TA) 11 on a downstream sideof the waste-heat-recovery heat exchanger 10, and temperatureinformation of oil from a temperature sensor (oil temperature sensor)(TO) 12 are inputted.

Based on the pieces of temperature information, the control device 30cools the oil injected to the compressor main body 3 to a propertemperature by changing the rotational frequency of the cooling fan 14by controlling the fan motor 15 via the inverter 29 such that atemperature difference of the delivery temperature of the compressed gasdetected by the delivery temperature sensor 5 from a previously settarget delivery temperature is small. The cooled oil is injected to thecompressor main body 3 via the oil filter 16.

That is, the rotation speed of the cooling fan 14 is controlled suchthat an amount of heat exchange at the cooling heat exchanger 13 isincreased in a case where the heat exchange amount at thewaste-heat-recovery heat exchanger 10 is small and such that the heatexchange amount at the air cooling heat exchanger 13 is reduced in acase where the heat exchange amount at the waste-heat-recovery heatexchanger 10 is large.

Each of heat exchanger capacities of the waste-heat-recovery heatexchanger 10 and the air cooling heat exchanger 13 is designed to be acapacity capable of processing a total heat amount generated at thecompressor main body 3 by itself. Therefore, in a case where maximumheat recovery is carried out in the waste-heat-recovery heat exchanger10, temperatures of the lubricant and the compressed air coming out fromthe waste-heat-recovery heat exchanger 10 are sufficiently cooled, andtherefore, there is also a case where the fan motor 15 is stopped in theair cooling heat exchanger 13.

In a case of an oil-cooled screw air compressor, a number of times ofcirculation of the oil filled in the compressor unit 20 (a number oftimes of circulation of returning the oil delivered from the compressormain body 3 again to the compressor main body) is generally as large asabout 2 through 5 times/minute, and therefore, when the rotation speedof the cooling fan 14 is changed, also the temperature of deliveredcompressed air detected by the delivery temperature sensor 5 iscomparatively sensitively changed. Therefore, the temperature of thecompressed air delivered from the compressor main body 3 cansubstantially be controlled to a target delivery temperature (deliverytemperature in a predetermined range) by carrying out an invertercontrol of changing the rotational frequency of the cooling fan 14 inaccordance with the temperature of the delivery temperature sensor 5.

Incidentally, according to the present embodiment, the temperaturesensor (TA) 11 and the temperature sensor (TO) 12 are provided, andtherefore, the temperature of the compressed air and the temperature ofthe oil flowing into the air cooling heat exchanger 13 are known, andtherefore, the rotation speed of the cooling fan 14 can also be adjustedby taking also pieces of temperature information from the temperaturesensors 11 and 12 into consideration, and the temperature of thecompressed air delivered from the compressor main body 3 can furtherswiftly and accurately be made to be proximate to a target temperature.

As described above, the compressor unit 20 can be operated such that thetemperature of the delivery temperature sensor 5 becomes constant,regardless of a waste-heat recovery situation (operating situation) ofthe stored hot water tank unit 23, that is, regardless of the heatexchange amount at the waste-heat-recovery heat exchanger 10 byexecuting the rotational frequency control of the cooling fan 14.

At inside of the stored hot water tank unit 23, there are provided atemperature sensor (heat medium temperature sensor) (Tw1) 25 fordetecting a temperature of the heat medium flowing through the heatmedium outlet piping 18 in the circulation pipings 17 and 18 circulatingthe heat medium between the waste-heat-recovery heat exchanger 10 andthe hot-water storage tank 19, a temperature sensor (hot watertemperature sensor) (Tw2) 26 for detecting a hot water temperature inthe hot-water storage tank 19, and a control device 31. The controldevice 31 is inputted with temperature information of the temperaturesensor 25 and the temperature sensor 26, and the control device 31 isconfigured to execute the control of the circulation pump 22 based onthe pieces of temperature information. For example, in a case where thetemperature detected by the temperature sensor (Tw2) 26 exceeds apreviously determined temperature (for example, a requested temperatureat a hot water supply destination), the control device 31 controls tostop the circulation pump 22 or reduce the rotational frequency.

Also, in a case where the temperature detected by the temperature sensor(Tw1) 25 is lower than the temperature detected by the temperaturesensor (Tw2) 26, or lower by a predetermined temperature or more, thereis a concern of lowering the hot water temperature in the hot-waterstorage tank 19, and therefore, also in this case, the circulation pump22 may be stopped, or its rotational frequency may be reduced.

Further, the control device 31 can be made to have a function as outputterminals for outputting the pieces of temperature information inputtedfrom the temperature sensors 25 and 26 to outside. That is, based on thetemperature information of the temperature sensors 25 and 26 outputtedfrom the control device 31, the pieces of temperature information can beused for hot water control at the water inlet piping 27 and the hotwater outlet piping 28. For example, in a case where the temperaturedetected by the temperature sensor (Tw2) 26 is equal to or higher than apreviously determined temperature (requested temperature at hot watersupply destination), it can be controlled such that hot water issupplied to the supply destination by opening a valve (not illustrated)provided at the hot water output piping 28, at the same time, water canbe replenished into the hot-water storage tank 19 by also opening avalve (not illustrated) provided at the water inlet piping 27.

Further, the pieces of temperature information from the temperaturesensors 25 and 26 can also be outputted from the control device 31 to anexternal display device, or a control device 32, to be described later,for controlling a total of the waste-heat recovery system.

Numeral 32 designates a control device for controlling the total of thewaste-heat recovery system in the oil-cooled gas compressor shown inFIGS. 1, and the control device 32 is provided in the stored hot watertank unit 23, or in the compressor unit 20. Further, the control device32 is inputted with information of an oil temperature detected by thetemperature sensor (TO) 12, and information of hot water temperature inthe hot-water storage tank 19 detected by the temperature sensor (Tw2)26, and controls to stop the circulation pump 22, or to reduce itsrotational frequency in a case where the temperature detected by thetemperature sensor 12 is equal to or lower than the temperature detectedby the temperature sensor 26.

Incidentally, the control device 32 is configured to be able to inputalso a piece of information of the compressed gas temperature detectedby the temperature sensor (TA) 11 via the control device 30, andtherefore, in a case where the temperature detected by the temperaturesensor 11 is equal to or lower than the temperature detected by thetemperature sensor 26, the circulation pump 22 may be controlled tostop, or its rotational frequency may be controlled to reduce.

Also, the control device 32 can be made to have a function as an outputterminal for outputting temperature information inputted from thetemperature sensor (TA) 11, the temperature sensor (TO) 12, and thetemperature sensor (Tw2) 26 to outside.

In a case where the compressor unit 20 is brought into a stoppage stateor a no-load operating state, the waste-heat recovery heat amount whichcan be received from the waste-heat-recovery heat exchanger 10 is small.Also, in a case where the temperature of the oil flowing in the oilpiping at the waste-heat-recovery heat exchanger 10 is lower than thehot water temperature in the hot-water storage tank 19, the heat in thehot-water storage tank 19 is moved to the waste-heat-recovery heatexchanger 10 via the heat medium flowing in the circulation circuits,and therefore, the waste-heat recovery rate is deteriorated.

In contrast thereto, according to the present embodiment, as describedabove, in a case where the temperature detected by the temperaturesensor (TO) 12 or the temperature sensor (TA) 11 is equal to or lowerthan the temperature detected by the temperature sensor (Tw2) 26, forexample, the circulation pump 22 is controlled to stop. Therefore,according to the present embodiment, deterioration in the waste-heatrecovery rate can be prevented.

Further, based on the temperature information outputted from the controldevice 32 to outside, the temperature information can also be used forcontrolling the water inlet piping 27 and the hot water outlet piping28. That is, in a case where the detected temperature of the temperaturesensor (TO) 12 or the temperature sensor (TA) 11 is equal to or lowerthan the detected temperature of the temperature sensor (Tw2) 26, afurther temperature rise of the hot water in the hot-water storage tank19 cannot be desired, and therefore, also in this case, the hot watermay be utilized by opening the valve provided at the hot water outletpiping 28, or water may be replenished into the hot-water storage tank19 by opening also the valve provided at the water inlet piping 27.

Incidentally, in the embodiment shown in FIG. 1, the description hasbeen given of the example of controlling to stop the circulation pump 22or lower the rotational frequency in a case where the temperature of theoil or the compressed gas subjected to heat exchange at thewaste-heat-recovery heat exchanger 10 is equal to or lower than thetemperature of the hot water in the stored hot water tank detected bythe hot water temperature sensor 26, but the control may be carried outas follows.

That is, in a case where the temperature of the oil or the compressedgas subjected to heat exchange at the waste-heat-recovery heat exchanger10 is equal to or lower than the temperature detected by the heat mediumtemperature sensor 25, the circulation pump 22 may be controlled to stopor the rotational frequency may be controlled to reduce by the controldevice 32.

That is, the hot water temperature sensor 26 detects a temperature on anupper side of the hot-water storage tank 19, and therefore, ordinarily,the temperature detected by the heat medium temperature sensor 25becomes a temperature substantially near to the temperature detected bythe hot water temperature sensor 26. Therefore, even when the control iscarried out by using the temperature detected by the heat mediumtemperature sensor 25, an effect substantially similar to that in a caseof controlling by using the hot water temperature sensor 26 is achieved.

Further, in a case where the compressor main body 3 is brought into thestoppage state or the no-load operating state, and in a state in whichthe temperature of the hot water in the hot-water storage tank 19 isthat in the midst of boiling, the temperature of the hot water in thehot-water storage tank 19 is high on the upper side and low on the lowerside. Therefore, the heat medium is subjected to heat exchange also withwater at a low temperature in the water-to-water heat exchanger 24, andtherefore, the temperature of the heat medium flowing in the heat mediuminlet piping 17 is lower than the temperature detected by the hot watertemperature sensor 26. In the state, there can be a case where thetemperature of the oil or the compressed gas in the waste-heat-recoveryheat exchanger 10 is lower than the temperature detected by the hotwater temperature sensor 26. However, even in the state, in a case wherethe temperature detected by the heat medium temperature sensor 25 islower than the temperature detected by the oil temperature sensor 12 orthe gas temperature sensor 11, the waste-heat recovery is carried out,and therefore, it is preferable to continue driving the circulation pump22.

On the other hand, in a case where the temperature detected by the oiltemperature sensor 12 or the gas temperature sensor 11 is lower than thetemperature detected by the heat medium temperature sensor 25, heat ismoved from the side of the heat medium to the side of the oil or thecompressed gas, and therefore, in this case, the circulation pump 22 isstopped. By controlling in this way, the waste-heat recovery rate can beimproved.

Further, according to the present embodiment, the explanation has beengiven of the example in which the control device 32 carries out thecontrol by comparing the detected temperature of the temperature sensor(TO) 12 or the temperature sensor (TA) 11, and the detected temperatureof the temperature sensor (Tw2) 26 or the temperature sensor (Tw1) 25.However, also the temperature information detected by the deliverytemperature sensor (T1) 5 is configured to be inputted to the controldevice 32 via the control device 30, and therefore, the controldescribed above can also be carried out by using the detectedtemperature of the delivery temperature sensor (T1) 5 in place of thetemperature sensor (TO) 12 or the temperature sensor (TA) 11, and asubstantially similar effect can be achieved also in this way. Further,a further accurate control can be carried out when the control iscarried out by using the detected temperatures of all of the temperaturesensors 5, 11, and 12.

Further, although according to the present embodiment, the example ofinstalling only the single piece of the hot water temperature sensor(Tw2) 26 at the upper portion of the hot-water storage tank 19 is shown,a position of installing the hot water temperature sensor 26 is notlimited to the upper portion but, for example, the hot water temperaturesensor 26 may be installed at a vicinity of a center portion.Preferably, the hot water temperature sensor 26 may be installed at aportion on an upper side of the water-to-water heat exchanger 24.Further, when plural hot water temperature sensors 26 are installed inan up and down direction in the hot-water storage tank 19, and thecontrol is carried out by using the plural temperature sensors, a wasteheat recovery system which can further improve the waste-heat recoveryrate can be established.

Further, in a case where the temperature detected by the deliverytemperature sensor 5 is lower than the temperature detected by at leasteither of the oil temperature sensor 12 or the gas temperature sensor11, it is believed that the temperature of the oil or the compressed gassubjected to heat exchange in the waste-heat-recovery heat exchanger 10is lower than the temperature of the hot water in the hot-water storagetank 19. Therefore, in a case where the temperature detected by thedelivery temperature sensor 5 is lower than the temperature detected byat least either of the oil temperature sensor 12 or the gas temperaturesensor 11, the control device 32 determines that the temperature of theoil or the compressed gas subjected to the waste-heat-recovery heatexchanger 10 is lower than the temperature of the hot water in thehot-water storage tank 19, and may stop the circulation pump 22 or mayreduce the rotational frequency.

FIG. 2 is a diagram showing a test result of a relationship between acooling water amount and a temperature rise of the passed cooling waterat the outlet of the waste-heat-recovery heat exchanger when thetemperature of the compressed gas delivered from the compressor mainbody 3 is made to be about 100° C. (in FIG. 2 described as “deliverytemperature 99° C.”) and when the cooling water is not circulated to thewaste-heat-recovery heat exchanger 10 by a number of times but is passedtherethrough only once in the waste-heat recovery system of theoil-cooled gas compressor shown in FIG. 1.

An explanation will be given of a specific effect of the temperaturerise at the waste-heat-recovery heat exchanger 10 according to thepresent embodiment by utilizing the test result of FIG. 2. The testresult is a result of carrying out a test in a waste-heat recoverysystem in which the hot-water storage tank 19 is not present in thewaste-heat recovery system shown in FIG. 1. The abscissa designates thecooling water amount flowing to the waste-heat-recovery heat exchanger10, and the ordinate designates the temperature rise of the hot waterafter passing through the waste-heat-recovery heat exchanger 10.Further, the diagram indicates the temperature (temperature rise) of thecooling water obtained by recovering waste heat combining a side of theoil piping 7 (side of oil cooler OC) and a side of the gas piping 8(side of air cooler AC) in the waste-heat-recovery heat exchanger 10.

As is known from FIG. 2, although the more reduced the cooling wateramount, the higher the temperature of the hot water obtained, at thecooling water amount equal to or less than 2 L/min, the temperature ofthe hot water cannot be elevated even when the cooling water amount isfurther reduced by a limit of a capability of the waste-heat-recoveryheat exchanger 10, the hot water temperature cannot be elevated evenwhen the cooling water amount is further reduced, and an elevation ofthe hot water temperature is up to a limit at 80° C. That is, in a casewhere the water is passed to the waste-heat-recovery heat exchanger 10only once (that is, case of 1 pass water passing), the temperature ofhot water obtained by waste-heat recovery from an oil-cooled screwcompressor (capacity of 22 kW is used in this example) in which thetemperature of the outlet of the compressor main body is set to be about100° C. has a limit of the temperature rise up to 80° C.

In contrast thereto, in a case of the waste-heat recovery system in theoil-cooled gas compressor shown in FIG. 1, water (hot water) iscirculated between the hot-water storage tank 19 and thewaste-heat-recovery heat exchanger 10 by a number of times via thecirculation piping 17 and 18, and therefore (because not water passingby only once but multi-pass water passing of circulating by a number oftimes), the temperature in the hot-water storage tank 19 can finally beelevated to a temperature near to the delivery temperature of thecompressor, for example, about 93° C. That is, in comparison with thecase of the water passing by only once (1 pass water passing) under thesame condition, the hot water at a high temperature of about 93° C. inwhich the temperature is higher by more than 10° C. can be obtained.Also, in a case where the water is passed to the waste-heat-recoveryheat exchanger 10 only once, when the load factor of the compressor islow, also the temperature of the hot water obtained is lowered. However,the compressor can maintain the delivery temperature basicallyregardless of the load factor, and therefore, the hot water at arequested temperature can be supplied regardless of the load factor ofthe compressor by constructing the configuration of the presentembodiment described above.

FIG. 3 is a diagram showing a test result of a relationship between thecooling water amount and the waste-heat recovery rate by the coolingwater passed when the temperature of the compressed gas delivered fromthe compressor main body 3 is made to be about 78° C., and the coolingwater is not circulated to the waste-heat-recovery heat exchanger 10 bya number of times but is passed therethrough only once in the waste-heatrecovery system. of the oil-cooled gas compressor shown in FIG. 1.

FIG. 3 shows a result of carrying out a test in a waste-heat recoverysystem in which the hot-water storage tank 19 is not present in thewaste-heat recovery system shown in FIG. 1 similar to FIG. 2. Theabscissa designates the cooling water amount to the waste-heat-recoveryheat exchanger, and the ordinate designates the waste-heat recovery rateby passing the cooling water to the waste-heat-recovery heat exchanger10. Also, the diagram indicates the waste-heat recovery rate byrecovering the waste-heat combining a side of the oil piping 7 (side ofoil cooler OC) and a side of the gas piping 8 (side of air cooler AC) inthe waste-heat-recovery heat exchanger 10. Here, the waste-heat recoveryrate is a value of the heat amount received by the waste-heat-recoveryheat exchanger 10 divided by a total input of the compressor, and thehigher the waste-heat recovery rate, the more effectively utilized thecompressor waste-heat.

As is known from FIG. 3, the more reduced the cooling water amount, thelower the waste-heat recovery rate, and at the cooling water amount of 2L/min at which the highest hot water temperature can be ensured in FIG.2 described above, as shown in FIG. 3, the waste-heat recovery rate isonly about 10%, and it is known that the efficiency of recovering thewaste-heat is very poor. That is, in a case of generating hot water bypassing the water therethrough only once and in a case where the hotwater at a high temperature to some degree is requested, it is necessaryto reduce the cooling water amount, and therefore, the waste-heatrecovery rate is very low.

Conversely, when the cooling water amount is increased, at a coolingwater amount to some degree or more (in FIG. 3, equal to or more than 10L/min), the waste-heat recovery rate can be increased near to 80%, andalthough even when the cooling water is increased more, the waste-heatrecovery rate cannot be increased more, the waste-heat recovery rate canbe maintained at a high value. That is, in view of the test result ofFIG. 3, the heat exchange can be carried out at a high waste-heatrecovery rate by making the cooling water amount equal to or more than10 L/min (for example, 20 L/min). Therefore, according to the presentembodiment shown in FIG. 1, not only hot water at a high temperature canbe obtained, but the waste-heat recovery system having the highwaste-heat recovery rate can be established by setting the cooling wateramount (for example, circulation water amount of 20 L/min).

Next, an explanation will be given of an application case in a case ofapplying the present invention to a cleaning facility by hot water. Theapplication example of the cleaning facility is a facility provided withtwo heaters of 5 kW in a background art, a temperature of water of 300 Lis elevated from 20° C. to 80° C. or higher by conducting electricitythereto, and cleaning is carried out by the obtained hot water. Here,when a calculation is made by assuming that all of the heat amount byconducting electricity to the heaters is used for elevating thetemperature of water, a time period required for elevating thetemperature to 80° C. or higher becomes about two hours. However, in anactual facility, heat was emitted naturally to the atmosphere, andtherefore, the temperature of the water was elevated to that of the hotwater having a target temperature of 80° C. or higher by conductingelectricity for 2.5 hours or longer. Further, ON/OFF of the heater of 5kW was repeated for keeping the temperature of the hot water at 80° C.or higher even in an operation of eight hours per day. Thereby, in thebackground art, a total of the power of about 47 kWh was consumed.

The example of applying the present invention to the cleaning facilityby the hot water will be explained. An oil-cooled screw air compressorunit (air cooling type) having a capacity of 22 kW has conventionally beinstalled on a side of the cleaning facility. Hence, a system ofproducing hot water used in the cleaning facility by utilizing thewaste-heat of the compressor unit was investigated, and the hot waterwas produced as the waste-heat recovery system as shown in FIG. 1. Acirculation amount of water (hot water) from the hot-water storage tank19 to the waste-heat-recovery heat exchanger 10 shown in FIG. 1 was madeto be 20 L/min.

Thereby, as has been explained in reference to FIG. 3, the heat recoveryrate as high as 80% was achieved, a time period required for elevating atemperature of water of 300 L from 20° C. to 80° C. or higher was 120minutes (two hours), and a target temperature was reached 30 minutesearlier than that of the background art using the heater. Further, afterreaching the target temperature of 80° C., the target temperature of 80°C. or higher could be kept by the compressor waste-heat, and therefore,a used power amount of 47 kWh per day in utilizing the heater of thebackground art could be brought to be 0 kWh. Further, high temperaturewater at 80° C. or higher could be obtained. This is achieved byapplying the present invention of circulating the hot water in thestored hot water tank to the waste-heat-recovery heat exchanger by anumber of times, and the temperature is difficult to be reached when thewater is passed to the waste-heat-recovery heat exchanger only once.

Second Embodiment

An explanation will be given of a second embodiment of a waste-heatrecovery system in an oil-cooled gas compressor according to the presentinvention in reference to a system diagram shown in FIG. 4. In FIG. 4,portions attached with notations the same as those of FIG. 1 describedabove indicate the same or corresponding portions, and therefore, theexplanation will be given centering on portions different from the firstembodiment shown in FIG. 1.

In the first embodiment described above, the explanation has been givenof the example in which the water-to-water heat exchanger 24 is providedin the hot-water storage tank 19, and the heat medium circulating to thecirculation circuits 17 and 18 are made to pass through thewater-to-water heat exchanger 24 to thereby subject the heat medium toheat exchange with water (hot water) in the hot-water storage tank 19.

In contrast thereto, the second embodiment differs from the firstembodiment in that the water-to-water heat exchanger 24 shown in FIG. 1is not provided, and the heat medium for circulating through thecirculation circuits 17 and 18 is made to be water (as water, a case ofhot water is also included) in the hot-water storage tank 19.

That is, water in the hot-water storage tank 19 of the stored hot watertank unit 23 is configured to be guided from a lower portion of thehot-water storage tank 19 directly to the heat medium inlet piping 17,and is sent to the waste-heat-recovery heat exchanger (water-cooled heatexchanger) 10 of the waste-heat recovery unit 21 by the circulation pump22. The water (heat medium) sent to the waste-heat-recovery heatexchanger 10 is subjected to heat exchange with the oil at a hightemperature flowing through the oil piping 7 and the compressed gas at ahigh temperature flowing through the gas piping (air piping) 8 in thewaste-heat-recovery heat exchanger and is heated by recovering heat fromthe oil and the compressed gas.

The oil and the compressed gas the heat of which is recovered by waterto be cooled are configured to be sent to the air cooling heat exchanger13 installed on the downstream side via the oil piping 7 or the gaspiping 8 to further be cooled. Further, the water (hot water) thetemperature of which is elevated by being heated by thewaste-heat-recovery heat exchanger 10 is returned to the hot-waterstorage tank 19 via the heat medium outlet piping 18. In this way, thewater in the hot-water storage tank 19 is circulated to thewaste-heat-recovery heat exchanger 10 repeatedly. Therefore, thetemperature of water in the hot-water storage tank 19 can gradually beelevated.

Thereby, the temperature of the water in the hot-water storage tank 19can be elevated to a previously determined prescribed temperature.Further, even in a case where the load factor of the air compressor isreduced, hot water at a requested temperature can be supplied regardlessof the load factor, and therefore, even in a case where there is arequested lower limit temperature of the hot water as well as therequested temperature is lower than the compressor deliver temperatureby several degrees, the hot water at the requested temperature can besupplied.

Even the configuration as in the second embodiment can achieve an effectsimilar to that of the first embodiment. Also, according to the secondembodiment, it is not necessary to provide the water-to-water heatexchanger as shown in the first embodiment, and therefore, its structureis simplified and the configuration can inexpensively be fabricated, andthe waste-heat recovery rate can be improved by an amount of dispensingwith heat exchange by the water-to-water heat exchanger.

Further, water can be subjected to heat exchange at thewaste-heat-recovery heat exchanger 10 by guiding water from the lowestportion in the hot-water storage tank 19, and therefore, the water atthe lowest temperature in the hot-water storage tank 19 and the oil andthe compressed gas at high temperatures from the compressor aresubjected to heat exchange, and therefore, the waste-heat recovery ratecan further be improved.

Other configuration or control is similar to that of the firstembodiment, and therefore, an explanation thereof will be omitted.

As has been explained above, according to the respective embodiments ofthe present invention, there is provided the waste-heat-recovery heatexchanger 10 for recovering heat from at least either of the compressedgas flowing through the gas piping 8 or the oil flowing through the oilpiping 7; further, there are provided the hot-water storage tank 19 forstoring heat received from the waste-heat-recovery heat exchanger 10 ashot water, the circulation circuits (circulation pipings 17 and 18) forcirculating the heat medium (fluid of water or the like) between thewaste-heat-recovery heat exchanger 10 and the hot-water storage tank 19for moving the heat received from the waste-heat-recovery heat exchanger10 to the hot-water storage tank 19, the circulation pump 22 provided atthe circulation circuits, and the control device for controlling to stopthe circulation pump or reduce its rotational frequency in a case wherethe temperature of the oil or the compressed gas subjected to heatexchange at the waste-heat-recovery heat exchanger is equal to or lowerthan the temperature of the hot water in the stored hot water tank.

Therefore, there can be provided the waste-heat recovery system in theoil-cooled gas compressor which can supply hot water at a requestedtemperature even in a case where the compressor load factor is low, andwhich can improve the waste-heat recovery rate by restraining heatemission from the waste-heat recovery apparatus.

That is, according to the present embodiments, as a cooling system ofthe oil-cooled gas compressor, in addition to the air cooling heatexchanger 13 which is the main first cooling system, thewaste-heat-recovery heat exchanger 10 which is a second cooling systemis provided, and the stored hot water tank unit (waste-heat recoveryapparatus) 23 is provided along with the compressor unit 20 to therebyconfigure a waste-heat recovery system, and the heat medium (in theembodiment described above, water) is made to be circulated by a numberof times between the hot-water storage tank 19 and thewaste-heat-recovery heat exchanger 10 via the circulation pipings 17 and18. Therefore, the temperature of the hot water in the hot-water storagetank 19 can be elevated up to a temperature lower than the compressoroutlet temperature by several ° C. (temperature near to compressoroutlet temperature).

The outlet temperature of the oil-cooled screw compressor is as low as100° C. or lower, and therefore, in a case of producing hot water by itswaste heat, the temperature is further lowered by a limit of the heatexchanger. However, the temperature of the hot water extremely near tothe compressor outlet temperature can be achieved by adopting thepresent embodiment.

Further, the control device controls to stop the circulation pump 22 orlower its rotational frequency in a case where the temperature of theoil or the compressed gas subjected to heat exchange at thewaste-heat-recovery heat exchanger 10 is equal to or lower than thetemperature of the hot water in the hot-water storage tank 19, andtherefore, the waste-heat recovery rate can also be restrained frombeing deteriorated by moving heat in the hot-water storage tank 19 tothe waste-heat-recovery heat exchanger 10 via the heat medium flowingthrough the circulation circuits.

Further, according to the present embodiments, the cooling fan 14 forblowing wind to the air cooling heat exchanger 13 in the compressor unit20 is configured to be able to control the rotational frequencyregardless of a heat exchange amount at the waste-heat-recovery heatexchanger 10, that is, regardless of operating situation of the storedhot water tank unit (waste-heat recovery apparatus) 23, and therefore,the outlet temperature of the compressor main body 3 can be controlledto be a constant target temperature. Therefore, there can be provided awaste-heat recovery system in an oil-cooled gas compressor in which itis not necessary to make the operating situation of the stored hot watertank unit (waste-heat recovery apparatus) 23 and the operating situationof the compressor unit 20 coincide with each other.

Further, the present invention is not limited to the embodimentsdescribed above but includes various modified examples.

For example, although in the respective embodiments described above, theexplanation has been given by taking an example of the air-cooled typescrew air compressor as the oil-cooled gas compressor, the presentinvention is not limited thereto but can similarly be applied even to acompressor of other system, for example, a scroll compressor.

Further, also a medium compressed by the oil-cooled gas compressor isnot limited to air but the present invention can similarly be applied toa compressor which compresses other gas. Further, also as a drivesource, other drive source other than a motor, for example, an engine ora turbine or the like will do.

Further, although in the embodiments described above, the explanationhas been given of the waste-heat recovery system in the oil-cooled gascompressor by the example in which three units of the compressor unit20, the waste-heat recovery unit 21, and the stored hot water tank unit23 are arranged in parallel and connected, the three units can beintegrated to configure one unit or two units.

Further, the embodiments described above have been explained in detailsfor explaining the present invention to be easy to understand, and thepresent invention is not necessarily limited to provide all of theconfigurations explained.

List of Reference Signs

-   1: suction filter-   2: suction throttle valve-   3: compressor main body-   4: main motor-   5: delivery temperature sensor (compressor main body outlet    temperature sensor)-   6: oil separator (oil tank)-   7: oil piping-   8: gas piping (air piping)-   9: temperature control valve-   10: waste-heat-recovery heat exchanger (water-cooled heat exchanger)-   11: temperature sensor (gas temperature sensor) (TA)-   12: temperature sensor (oil temperature sensor) (TO)-   13: air cooling heat exchanger-   14: cooling fan-   15: fan motor-   16: oil filter-   17, 18: circulation pipings (circulation circuits) (17: heat medium    inlet piping, 18: heat medium outlet piping)-   19: stored hot water tank-   20: compressor unit-   21: waste-heat recovery unit-   22: circulation pump-   23: stored hot water tank unit (waste-heat recovery apparatus)-   24: water-to-water heat exchanger-   25: temperature sensor (heat medium temperature sensor) (Tw1)-   26: temperature sensor (hot water temperature sensor) (Tw2)-   27: water inlet piping-   28: hot water outlet piping-   29: inverter-   30 through 32: control devices

1. A waste-heat recovery system in an oil-cooled gas compressorincluding a compressor main body, an oil separator for separating oilfrom compressed gas delivered from the compressor main body, a gaspiping for sending the compressed gas separated from the oil by the oilseparator to a demanded destination, an oil piping for returning the oilseparated by the oil separator to the compressor main body, and awaste-heat-recovery heat exchanger for recovering heat from at leasteither of the compressed gas flowing through the gas piping or the oilflowing through the oil piping, the waste-heat recovery system in theoil-cooled gas compressor comprising: a stored hot water tank forstoring the heat from the waste-heat-recovery heat exchanger in a formof hot water; a circulation circuit for circulating a heat mediumbetween the waste-heat-recovery heat exchanger and the stored hot watertank for moving the heat received from the waste-heat-recovery heatexchanger to the stored hot water tank; a circulation pump provided atthe circulation circuit; and a control device for controlling to stopthe circulation pump or reduce the rotational frequency thereof in acase where a temperature of the oil or the compressed gas subjected toheat exchange by the waste-heat-recovery heat exchanger is equal to orlower than a temperature of the hot water in the stored hot water tank.2. The waste-heat recovery system in an oil-cooled gas compressoraccording to claim 1, comprising a hot water temperature sensor fordetecting the temperature of the hot water in the stored hot water tank;wherein the control device stops the circulation pump or reduces therotational frequency thereof in a case where the temperature of the oilor the compressed gas subjected to the heat exchange by thewaste-heat-recovery heat exchanger is equal to or lower than thetemperature of the hot water in the stored hot water tank detected bythe hot water temperature sensor.
 3. The waste-heat recovery system inthe oil-cooled gas compressor according to claim 1, comprising a heatmedium temperature sensor for detecting a temperature of the heat mediumof the circulation circuit between the waste-heat-recovery heatexchanger and the stored hot water tank; wherein the control devicestops the circulation pump or reduces the rotational frequency thereofin a case where the temperature of the oil or the compressed gassubjected to the heat exchange at the waste-heat-recovery heat exchangeris equal to or lower than the temperature detected by the heat mediumtemperature sensor.
 4. The waste-heat recovery system in the oil-cooledgas compressor according to claim 2, comprising at least any of: adelivery temperature sensor for detecting a temperature on a deliveryside of the compressor main body; an oil temperature sensor fordetecting the temperature of the oil on an outlet side of thewaste-heat-recovery heat exchanger; and a gas temperature sensor fordetecting the temperature of the compressed gas on the outlet side ofthe waste-heat-recovery heat exchanger; wherein the circulation pump isstopped or the rotational frequency thereof is reduced in a case wherethe temperature detected by at least any of the delivery temperaturesensor, the oil temperature sensor, and the gas temperature sensor isequal to or lower than the temperature detected by either of the hotwater temperature sensor or the heat medium temperature sensor.
 5. Thewaste-heat recovery system in the oil-cooled gas compressor according toclaim 3, comprising at least any of: a delivery temperature sensor fordetecting a temperature on a delivery side of the compressor main body;an oil temperature sensor for detecting the temperature of the oil on anoutlet side of the waste-heat-recovery heat exchanger; and a gastemperature sensor for detecting the temperature of the compressed gason the outlet side of the waste-heat-recovery heat exchanger; whereinthe circulation pump is stopped or the rotational frequency thereof isreduced in a case where the temperature detected by at least any of thedelivery temperature sensor, the oil temperature sensor, and the gastemperature sensor is equal to or lower than the temperature detected byeither of the hot water temperature sensor or the heat mediumtemperature sensor.
 6. The waste-heat recovery system in the oil-cooledgas compressor according to claim 1, comprising: a delivery temperaturesensor for detecting a temperature on a delivery side of the compressormain body; and at least either of an oil temperature sensor fordetecting the temperature of the oil on an outlet side of thewaste-heat-recovery heat exchanger or a gas temperature sensor fordetecting a temperature of the compressed gas on the outlet side of thewaste-heat-recovery heat exchanger; wherein in a case where thetemperature detected by the delivery temperature sensor is lower thanthe temperature detected at least either of the oil temperature sensoror the gas temperature sensor, the control device determines that thetemperature of the oil or the compressed gas subjected to heat exchangeby the waste-heat-recovery heat exchanger is equal to or lower than thetemperature of the hot water in the stored hot water tank, and stops thecirculation pump or reduces the rotational frequency.
 7. The waste-heatrecovery system in the oil-cooled gas compressor according to claim 1;wherein a water-to-water heat exchanger is provided in the stored hotwater tank, and the heat medium of the circulation circuit is configuredto pass through the water-to-water heat exchanger and is subjected toheat exchange with water (hot water) in the stored hot water tank. 8.The waste-heat recovery system in the oil-cooled gas compressoraccording to claim 1, wherein the heat medium circulating through thecirculation circuit is water (hot water) in the stored hot water tank.9. The waste-heat recovery system in the oil-cooled gas compressoraccording to claim 1, comprising a hot water temperature sensor fordetecting a temperature of the hot water in the stored hot water tank;wherein the control device is configured to allow supplying the hotwater to a supply destination when the temperature of the hot water inthe stored hot water tank detected by the hot water temperature sensoris equal to or higher than a prescribed temperature (requested lowesttemperature).
 10. The waste-heat recovery system in the oil-cooled gascompressor according to claim 1, comprising: an air cooling heatexchanger provided on a downstream side of the waste-heat-recovery heatexchanger for cooling the compressed gas flowing through the gas pipingand a lubricant flowing through the oil piping; and a cooling fan forblowing a cooling wind to the air cooling heat exchanger; wherein therotational frequency of the cooling fan is controlled such that thetemperature of the compressed gas delivered from the compressor mainbody falls in a prescribed range.